Efficient energy transfer mediated by intrinsic SiO2 nanocrystals in Eu+3-doped lead borosilicate glasses

Lead borosilicate glass (SiO2–B2O3–PbO2) doped with different Eu3+ ion concentrations have been synthesized by fusion method and characterized through optical absorption, photoluminescence (PL) and time-resolved PL spectra in the temperature range from 15 to 300 K. The PL spectra show characteristic ions Eu3+ transitions followed by a red emission at 695 nm and a green emission at 550 nm. The red and green emissions were associated with a non-bridging oxygen hole center (NBOHC) and OH groups stabilized on the SiO2 nanocrystal surface, respectively. Atomic Force Microscopy images confirm a precipitated crystalline phase with size of 21 nm in the glass matrix. Inhibition of the intrinsic nano-crystallization process of the SBP glass template has been observed as Eu3+ ions concentration increases. As sample temperature increases, an efficient energy transfer process from SiO2 nanocrystal surface states toward Eu3+ states takes place. This leads to a strong increase in the PL emission intensity of Eu3+ states followed by a decreasing PL peak intensity of the surface states. The energy transfer process leads also to an abnormal average lifetime of SBP:Eu3+ luminescent states with increasing temperature.